(a) Field of the Invention
The present invention relates to a hydraulic control system of an automatic transmission for a vehicle. More particularly, the present invention relates to a hydraulic control system of an automatic transmission for a vehicle that can be exempt from a damper clutch control solenoid valve such that a cost may be reduced.
(b) Description of the Related Art
Typically, an automatic transmission automatically controls its shifting operation. For such an automatic shifting control, a shift control apparatus controls hydraulic pressure of a plurality of solenoid valves depending on various vehicle running states such as a vehicle speed and a throttle valve opening.
If a driver moves a select lever to a desired shift range, a manual valve in a hydraulic control system realizes a line conversion. In this case, a hydraulic pressure supplied from an oil pump is supplied to friction elements operating in respective shift-speeds according to a duty control of solenoid valves.
As an example of such an automatic transmission, a hydraulic control system of an automatic transmission that enables four forward speeds and one reverse speed is hereinafter described with reference to FIG. 8. As shown in FIG. 8, a hydraulic pressure generated at a hydraulic pump 102 is controlled to a regulated pressure by a regulator valve 104. The regulated pressure of the regulator valve 104 is supplied to a manual valve 106, a reducing valve 108, a low-reverse brake (L-R/B) solenoid valve S1 (hereinafter called a first solenoid valve S1), a low-reverse brake (L-R/B) pressure control valve 10 (hereinafter called a first pressure control valve 110), and a damper clutch control valve 112. As shown in FIG. 8, the first solenoid valve S1 receives the regulated pressure of the regulator valve 104 as a control pressure. In addition, the first pressure control valve 10 is controlled by the first solenoid valve S1.
In addition, the manual valve 106 realizes hydraulic line conversion according to a range conversion of the select lever (not shown). By the manual valve 106, the hydraulic pressure supplied from the regulator valve 104 is supplied to a second brake (2ND/B) pressure control valve 114 (hereinafter called a second pressure control valve 114), an underdrive clutch (UD/C) pressure control valve 116 (hereinafter called a third pressure control valve 116), and an overdrive clutch (OD/C) pressure control valve 118 (hereinafter called a fourth pressure control valve 118).
In addition, the reduced hydraulic pressure of the reducing valve 108 is supplied to a second brake (2ND/B) solenoid valve S2 (hereinafter called a second solenoid valve S2), an underdrive clutch (UD/C) solenoid valve S3 (hereinafter called a third solenoid valve S3), and an overdrive clutch (OD/C) solenoid valve S4 (hereinafter called a fourth solenoid valve S4) that respectively control the second, third, and fourth pressure control valves 114, 116, and 118.
In addition, the reduced pressure of the reducing valve 108 is also supplied to a proportional control solenoid valve S5 that controls the regulator valve 104, such that the line pressure may be controlled by controlling the proportional control solenoid valve S5 depending on a driving condition of a vehicle.
The hydraulic pressures controlled at the first, second, third, and fourth pressure control valves 110, 114, 116, and 118 according to the control of the first, second, third, and fourth solenoid valves S1, S2, S3, and S4 are supplied to frictional elements, directly or through first and second fail-safe valves 120 and 122.
That is, the first solenoid valve S1 and the first pressure control valve 110 are connected with a low-reverse brake (L-R/B) that operates at a first forward speed and a reverse speed, through the first fail-safe valve 120. The second solenoid valve S2 and the second pressure control valve 114 is connected with a second brake (2ND/B) that operates at second and fourth forward speeds, through the second fail-safe valve 122.
In addition, the third solenoid valve S3 and the third pressure control valve 116 are directly connected with an underdrive clutch (UD/C) that operates at first, second, and third forward speeds. The fourth solenoid valve S4 and the fourth pressure control valve 118 are directly connected with an overdrive clutch (OD/C) that operates at third and fourth forward speed.
A reverse clutch (R/C) that operates at the reverse speed is directly connected with the manual valve 106.
In addition, the regulated hydraulic pressure of the regulator valve 104 is also supplied to a torque converter control valve 124 that controls a hydraulic pressure supplied to a torque converter (TC), and also supplied to damper clutch control valve 112 that controls a hydraulic pressure supplied to a damper clutch for enhancing power delivery efficiency of the torque converter (TC).
The damper clutch control valve 112 controls an on/off operation of the damper clutch according to a control of a damper clutch control solenoid valve (DCCSV).
By such an arrangement, the first, second, third, and fourth solenoid valves S1, S2, S3, and S4 are controlled by a transmission control unit (TCU) (not shown) so as to control the first, second, third, and fourth pressure control valves 100, 114, 116, and 118, such that each frictional element is supplied with or released from the supplied pressure depending on shift-speeds so as to realize multi-speeds.
Such a hydraulic control system employs a solenoid valve for controlling a damper clutch control valve, which causes an increase of a cost for an automatic transmission. Therefore, if an automatic transmission may be exempt from the solenoid valve for controlling the damper clutch control valve while maintaining substantially equivalent functioning of the transmission, it may contribute to reduction of the cost for manufacturing the transmission.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.